A COMPARISON  OF  THE  RESPONSES  OF 


SESSILE  AND  MOTILE  PLANTS 
AND  ANIMALS 


PROFESSOR  VICTOR  E.  SHELFORD 

<TY  Of  ILUK'VS 

• tw  2 5 1316 


NEW  YORK 
1914 


[Reprinted  without  change  of  paging,  from  the  American  Naturalist,  1914.] 


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[Reprinted  from  The  American  Naturalist,  Vol.  XLVIIL,  Nov.,  1914.] 


m 'i  Y Or  TlUfiOTS  Li'SRAf 

MOV  3 5 1916 


A COMPARISON  OF  THE  RESPONSES  OF 
SESSILE  AND  MOTILE  PLANTS 
AND  ANIMALS 

PROFESSOR  VICTOR  E.  SHELFORD, 

University  of  Illinois 


I.  Introduction  642 

II.  Basis  of  Discussion 642 

1.  Responses  . 643 

2.  Sessile  and  Motile  Organisms 644 

3.  The  Individual  and  its  Relation  in  Colonies  and  Groups 644 

(a)  Animals  and  Plants  made  up  of  Single  Individuals  ....  644 

(b)  Colonial  or  Multiple  Individualed  Plants  and  Animals.  645 

i.  Numbers  of  Individuals  645 

ii.  Stems 646 

iii.  Metabolic  and  Reproductive  Relations  of  Individ- 

uals   647 

( c ) Response  of  Motile  Organisms 649 

i.  Movements  649 

ii.  Structural  Response  650 

( d ) Response  of  Sessile  Organisms 651 

i.  Structural  Responses  651 

ii.  Movements  653 

(e)  Behavior  of  Sessile-motile  Organisms  653 

(/)  Response  and  Taxonomy  of  Sessile  Organisms 653 

III.  Parallelism  between  Sessile  and  Motile  Organisms  with  reference 

to  Ecology  654 

1.  Breeding 654 

2.  Comparison  of  Sessile  and  Motile  Elements  of  the  Biota  ....  655 

3.  Sessile  Motile  Organisms  in  Ecological  Succession 656 

IV.  Influence  of  Response  Phenomena  upon  Biological  Theory  and  Con- 

troversy   657 

1.  Teleological  View 657 

2.  Natural  Selection  View 658 

3.  Supposed  Non-inheritance  of  Response  and  the  Germ  Plasm 

Doctrine  660 

4.  Influence  of  the  Study  of  Response  on  Present-day  Biological 

Theory  661 

5.  Aspects  of  the  Untenability  of  the  Germ  Plasm  Doctrine.  . . . 662 

6.  Measure  of  Values  in  Biological  Science 664 

7.  Summary  and  Conclusions 669 

V.  Literature  Cited  672 


641 


EDMUND  J.  JAMES 


642 


THE  AMERICAN  NATURALIST  [Vol.  XLVIII 


I.  INTRODUCTION 

During  the  past  few  years  the  attention  of  biologists 
has  turned  more  and  more  from  those  phenomena  which 
were  supposed  to  be  comparatively  fixed,  to  responses  to 
stimuli.  Physiologists  have  long  been  concerned  with 
the  mechanism  of  response ; psychologists  are  interested 
in  its  modification.  Geographers,  climatologists  and 
ecologists  have  recently  turned  their  attention  to  re- 
sponses in  natural  environments  and  zoologists  have 
become  interested  in  response,  particularly  from  the  point 
of  view  of  its  specificity.  In  these  quite  independent 
investigations  and  compilations  there  has  been  little 
attempt  at  analysis  with  a view  to  determine  legitimate 
lines  of  comparison  among  the  exceedingly  diversified 
types  of  organisms  which  have  been  investigated,  and 
some  confusion  has  resulted.  For  example,  since  the 
more  obvious  responses  of  plants  are  structural,  persons 
not  familiar  with  comparable  phenomena  among  animals 
have  made  erroneous  comparisons  of  sessile  plants  and 
motile  animals.  This  paper  is  written  to  present  in  as 
nearly  uniform  terms  as  practicable  (a)  analysis  of  kinds 
or  aspects  of  response,  (b)  justifiable  kinds  of  compari- 
son, and  ( c ) the  bearing  of  response  phenomena  on 
biological  theory  and  controversy.  It  aims  to  show  that 
the  numerous  kinds  of  response  are  reducible  to  a few 
simple  types  common  to  both  plants  and  animals,  and  that 
the  failure  to  consider  all  types  has  been  responsible  for 
confusion  and  various  one  sided  theories.  It  further  aims 
to  show  that  study  of  response  during  the  past  few  years 
has  led  to  an  unusual  broadening  of  our  conceptions. 

II.  BASIS  OF  DISCUSSION 

As  a basis  for  discussion  we  must  first  have  a clear 
understanding  of  the  character  and  definition  of  response. 
Secondly,  we  must  determine  what  constitutes  an  indi- 
vidual in  those  plants  and  animals  that  are  made  up  of 
repetitions  of  parts.  Thirdly,  we  must  note  whether  or 
not  the  organism  is  sessile  or  motile,  capable  of  playing 
the  part  of  either,  or  colonial  pelagic. 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 

1.  Responses 

The  word  response  is  used  in  various  slightly  different 
senses.  In  general  it  refers  to  more  complex  and  time- 
requiring  phenomena  than  ‘ ‘ reaction.  ’ ’ In  geography  the 
term  has  been  used  (Goode,  ’04)  to  cover  all  changes  in 
culture  supposed  to  be  produced  by  climate  or  other 
geographic  conditions.  It  is  also  applied  by  geographers 
and  geologists  to  changes  in  the  physical  characteristics 
of  man  (evolution)  which  Goode  (’04)  has  stated  are 
slower  than  the  cultural  responses.  In  general  botanists 
have  used  the  term  to  cover  changes  of  plant  structure 
and  function  induced  by  external  conditions.  Cowles 
(’ll),  however,  uses  the  word  “reaction”  to  cover  these 
phenomena.  Coulter  (’09)  used  the  term  response  as 
synonymous  with  adaptation  in  plants.  Zoologists  have 
used  the  term  to  apply  to  changes  in  animals  due  to  exter- 
nal conditions,  but  with  little  agreement  as  to  what  is  to 
be  included.  We  will  use  it  here  to  include  reactions , 
changes  in  functions,  structure,  color,  induced  by  external 
conditions  either  directly  or  indirectly,  without  regard 
to  how  simple  or  how  complex  the  processes  involved 
may  be.1  The  length  of  time  required  to  bring  the 
changes  about  may  arbitrarily  be  taken  as  not  exceeding 
the  time  required  to  breed  five  to  ten  generations  of  the 
species  concerned.  All  organisms  respond  to  stimuli 
because  each  stimulus  acts  upon  some  internal  process. 
Strictly  speaking,  the  response  is  the  change  or  changes 
in  the  physical  or  chemical  processes  of  the  organism  (or 
the  part  or  parts  concerned)  which  results  from  the 
disturbance. 

Those  things  which  we  commonly  see  and  term  response 
are  often  the  later  and  less  important  phases  of  the  dis- 
turbance. The  striking  phases  of  responses  of  motile 
organisms  are  usually  movements  which  follow  closely 
upon  stimulation.  In  sessile  organisms  the  noticeable 
responses  often  appear  only  after  a considerable  period. 
In  both  sessile  and  motile  organisms  some  responses  are 

1 For  good  representative  bibliography  see  Adams,  ’33,  Ch.  VIII  and 
IX. 


644 


THE  AMEBIC  AN  NATURALIST  [Vol.  XLYIII 


not  evident  because  they  concern  internal,  chemical  and 
physical  processes  which  affect  neither  form  nor  move- 
ment. Changes  in  the  enzymes  secreted  by  digestive 
glands,  which  accompany  changes  in  food  (Jennings,  ’06, 
p.  347),  are  examples.  While  thus  recognizing  that  re- 
sponses are  concerned  primarily  with  internal  processes, 
we  must  of  necessity  refer  chiefly  to  the  external  phases. 

2.  Sessile  and  Motile  Organisms 

Sessile  organisms  are  those  which  are  sedentary  in 
habit,  whether  attached  or  possessing  slight  powers  of 
locomotion.  Motile  organisms  are  those  that  habitually 
move  about.  Vagile  or  creeping  forms  as  well  as  swim- 
ming, walking,  flying,  burrowing  types  are  included. 
Most  sessile  animals  are  capable  of  moving  their  parts, 
while  only  a few  sessile  plants  possess  this  capacity,  and 
these  only  to  a slight  degree. 

There  is  no  sharp  distinction  between  sessile  (seden- 
tary) and  motile  organisms.  Every  possible  gradation 
exists  between  fixed  non-motile  types  as  trees  on  the  one 
hand  and  the  pelagic  fishes  on  the  other.  It  is  the 
extremes  which  we  will  compare. 

3.  The  Individual  and  Its  Relations  in  Colonies 
and  Groups 

The  following  comparison  of  animals  and  plants  is  an 
attempt  to  distinguish  potential  or  incomplete  individuals 
in  colonial  organisms  and  compound  organisms  which, 
while  not  commonly  recognized  as  colonial,  are  made  up  of 
incomplete  individuals. 

(a)  Animals  and  Plants  made  up  of  Single  Individuals 

The  vast  majority  of  animals  belong  here.  Most  pro- 
tozoa, solitary  sponges,  solitary  hydroids,  sea  anemones, 
worms  not  preparing  for  asexual  division,  echinoderms, 
mollusks,  arthropods  and  vertebrates.  Only  single-celled 
plants,  young  seedlings  and  possibly  a few  adults  of  multi- 
cellular plants  which  possess  but  one  growing  point 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


645 


(exclusive  of  roots)  belong  in  this  group.  Single  indi- 
viduals as  described  here  are  the  basis  for  determining 
what  shall  be  called  individuals  in  colonial  and  compound 
types. 

( b ) Colonial  or  Multiple  Individualed  Plants  and  Animals 

A number  of  animals  and  the  vast  majority  of  the 
plants  belong  here.  The  group  can  be  roughly  divided 
into  two  types,  (a)  those  having  a chain  or  plate  arrange- 
ment of  incomplete  individuals  and  ( b ) those  having  a 
branching  or  tree-like  arrangement.  The  groups  of  in- 
complete individuals  of  type  a occur  among  the  Protozoa, 
worms  undergoing  asexual  reproduction,  many  of  the 
Bryozoa  and  some  of  the  Tunicates;  both  sessile  and 
pelagic  (plankton)  forms  occur.  On  the  plant  side  type 
a includes  plate-like  colonies  of  algae,  filamentous  algae, 
some  thallose  plants  and  probably  some  of  the  fungi, 
though  the  great  multiplicity  of  forms  makes  the  separa- 
tion of  this  group  from  the  branching  tree-like  types, 
difficult. 

Type  b includes  some  of  the  colonial  Protozoa,  the 
majority  of  the  sponges,  hydroids,  corals  and  the  branch- 
ing Bryozoa.  The  algae,  fungi,  mosses,  ferns  and  flower- 
ing plants  are  all  represented.  The  colonies  are  usually 
attached  to  the  substratum  (sessile). 

i.  Numbers  of  Individuals. — Among  the  animals  the 
number  of  so-called  zooids  is  the  number  of  incomplete 
individuals.  In  the  sponges  there  are  as  many  zooids  as 
there  are  excurrent  openings  (osculae)  (Minchins,  ’00, 
p.  91).  Zooids  usually  possess  a mouth  opening  and 
organs  for  securing  food,  though  in  some  cases  they  may 
be  specialized  for  reproduction,  defence  or  locomotion  as 
in  some  of  the  Coelenterates.  Among  the  colonial  plants 
there  are  as  many  incomplete  individuals  as  there  are 
buds  or  growing  points  (vegetative  regions).  There  are 
no  regularly  occurring  organs  in  animals,  strictly  com- 
parable to  leaves.  However,  any  organs  such  as  tentacles, 
gills,  etc.,  which  secure  or  absorb  nutriment  may  be  re- 


646  the  AMEBIC  AN  NATURALIST  [Vol.XLVIII 

garded  as  analogous  to  leaves.  Each  potential  bud  with 
its  leaf  may  be  compared  to  a zooid.  In  comparing  plants 
and  animals,  roots  can  perhaps  be  compared  with  the 
holdfast  organs  of  hydroids.  In  both  groups,  roots  and 
root-like  organs  are  individuals  of  a very  low  order  of 
individualization  and  of  a type  not  well  represented 
among  animals.  The  holdfast  organs  of  animals  are  not 
important  absorbers  of  food  and  water. 

ii.  Stems  and  Other  Connecting  Organs  ( Conducting 
Tissues). — The  most  striking  difference  between  the  in- 
complete individuated  or  colonial  plants  and  colonial  ani- 
mals is  the  presence  in  the  former  of  specialized  stems  and 
highly  complex  conducting  tissues  (Cowles,  ’ll;  Putter, 
Ml,  pp.  361-66).  The  conduction  of  food  materials  from 
the  root  to  other  parts  of  the  plant  and  from  the  leaves  to 
the  root  is  a functional  necessity  not  paralleled  even  in 
those  colonial  animals  showing  the  greatest  division  of 
labor.  In  animals  stems  are  relatively  undifferentiated 
and  are  often  made  up  of  living,  relatively  unspecialized 
zooids,  as,  for  example,  in  many  Bryozoa  such  as  Crisis. 
The  tendency  to  cauliflory  in  some  plants  and  the  ability 
of  cambium  to  produce  shoots  and  of  the  stems  of  most 
hydroids  to  produce  individuals  indicates  that  such  a con- 
dition may  be  potentially  present  in  all.  In  stalked 
Protozoa  the  stems  are  solid,  while  in  most  Coelenterates 
they  are  tubes,  usually  simple  though  sometimes  complex, 
made  up  by  mere  elongation  and  branching  of  the  stock 
of  the  simple  single  forms  such  as  the  Hydra.  The  lumen 
is  usually  ciliated  and  makes  possible  a transfer  of  mate- 
rial which  renders  practicable  such  division  of  labor  as 
occurs  in  this  group  (Putter,  Ml).  In  the  Bryozoa  the 
different  zooids  have  their  body  cavities  joined  in  the 
simpler  forms  merely  as  a branching  lumen  of  the  main 
wall  of  the  colony;  in  others  by  small  openings  the  more 
specialized  of  which  are  sieve-like  plates  (Harmer,  ’01, 
pp.  471  and  496;  Delage  and  Herouard,  ’97,  Yol.  5,  p.  62). 

The  connection  between  the  individuals  of  the  tunicate 
colonies  is  often  very  complex,  due  to  the  fact  that  in  the 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


647 


most  complex  types  the  stolon  (stem)  gives  rise  to  new 
individuals  and  possesses  all  the  layers  of  cells  which 
take  part  in  forming  them.  The  connection  between 
different  individuals  differs  in  different  groups  and  is 
determined  by  the  particular  mode  of  asexual  reproduc- 
tion. As  the  individuals  are  quite  independent  of  one 
another  in  function,  these  connections  do  not  have  the 
same  significance  as  in  plants.  Even  where  there  is  a 
common  blood  circulation,  as  for  example  in  the  Clavel- 
linidce  (Harmer,  ’04,  p.  71),  there  is  no  noteworthy  divi- 
sion of  labor. 

iii.  Metabolic  and  Reproductive  Relations  of  Individ- 
uals.— The  flat  worms  at  certain  times  consist  of  chains 
of  zooids  at  various  stages  of  development  and  with 
various  degrees  of  independence.  Child  ( ’13)  has  found 
that  these  chains  of  zooids  present  a series  of  gradients 
in  rate  of  metabolic  reaction.  The  rate  is  highest  at  the 
anterior  end  of  the  whole  chain  and  decreases  toward  the 
posterior  end,  not  uniformly,  however,  for  the  rate  is 
lower  immediately  in  front  of  each  head  region  than  it 
is  in  the  head  region  itself.  A gradient  is  present  in  the 
axis  of  each  zooid.  The  most  anterior  head  dominates  so 
long  as  the  chain  remains  intact.  In  the  corals  certain 
zooids  dominate  (Wood-Jones,  ’ll)  over  the  others. 
Some  types  have  a single  dominant  zooid  and  some  more, 
while  in  other  cases  all  are  equal. 

Among  plants  whose  form  is  that  of  a chain  or  a plate 
the  individuals  are  less  closely  bound  together  and  domi- 
nant vegetative  regions  are  probably  less  well  developed. 
In  the  branching  types,  dominant  vegetative  regions  occur 
(Cowles,  ”11,  p.  747 ; Goebel,  ’00,  Vol.  I,  p.  206).  In  the 
conifers,  for  example,  there  is  a leader,  a dominant  grow- 
ing region  at  the  tip  of  the  main  stem  just  as  in  certain 
madrepore  corals  (Wood-Jones,  p.  83).  Other  plants  like 
the  elm  have  several  vegetative  regions  which  dominate 
over  others,  as  they  do  in  the  branching  madrepores. 

Growth  form  or  colony  form  varies  according  to  cer- 
tain laws  dependent,  in  part  at  least,  upon  the  metabolic 


648 


THE  AMERICAN  NATURALIST  [Vol.  XLYIII 


relations  of  individuals.  Thus  Wood- Jones  says  of  the 
corals — 

a colony  may  grow  according  to  five  different  types  of  vegetative  growth 
. . . it  may  grow  as  (1)  a spherical  mass,  (2)  an  encrusting  layer,  (3)  a 
free  plate,  (4)  a branching  tree-like  growth,  or  (5)  a mere  amorphous 
lump. 

He  further  notes  the  division  of  all  the  corals  into  two 
groups  of  normal  growth-forms ; for  all  the  zooids  may 
take  an  equal  share  in  the  asexual  reproduction  or,  again, 
some  may  he  of  greater  importance  than  others , and  the 
asexual  reproductive  functions  may  he  lodged  in  a very 
few  individuals  only.  Considering  the  first  division 
(all  zooids  taking  equal  share,  the  principal  types  of  bud- 
ding vary  from  each  other  in  the  actual  site  of  origin  of 
the  daughter  zooid  from  the  parent,  in  the  degree  of  final 
separation  of  the  two  zooids,  and  in  the  thickess  of  the 
intervening  partition  between  the  two  zooids.  The 
amount  of  rising  above  the  general  surface  by  each  indi- 
vidual zooid  is  likewise  subject  to  variation. 

Turning  now  to  the  corals  that  constitute  the  second 
class  (some  zooids  of  greater  importance  than  others) 
which  in  the  words  of  Wood- Jones  have  some  of  their 
units  specialized  as  active  agents  of  growth, 

it  is  at  once  seen  that  the  possibilities  of  variation  of  normal  vegetative 
habit  are  greatly  increased.  All  the  elaborate  branching  forms,  plates 
and  leaf-like  growths  belong  to  this  class ; and  all  are  evolved  by  special 
peculiarities  of  the  growing  point.  The  zooids  that  constitute  the  grow- 
ing point  may  take  various  forms ; they  may  be  arranged  as  a cluster,  as 
a creeping  edge,  or  as  many  varieties  of  terminal  shoots  of  branches. 

In  the  first  instance,  it  is  necessary  to  draw  very  sharp  distinctions 
between  two  subdivisions  of  this  group.  In  Group  1 come  all  those 
forms  like  Montipora,  whose  distal  zooids  are  the  newest  formed  mem- 
bers of  the  colony;  and  in  Group  2 are  included  the  Madrepora,  whose 
distal  zooid  is  the  most  ancient  individual  in  the  whole  group. 

In  dealing  with  Group  1 many  forms  have  to  be  considered,  for  when 
the  youngest  are  the  active  zooids  their  growth  cluster  may  be  variously 
disposed,  and  on  its  disposition  the  resulting  vegetative  form  entirely 
depends. 

In  Group  2,  however,  this  state  of  things  is  entirely  altered,  for  there 
one  zooid,  which  is  situated  at  the  extremity  of  the  stem,  and  which  I 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


649 


shall  call  throughout  the  c(  dominant  apical  zooid”  constitutes  the  grow- 
ing point;  and  this  zooid  is  the  parent  of  the  entire  colony. 

Various  writers  make  comparable  statements  or  show 
comparable  principles  among  hydroids  (Motz-Kossowska, 
’08)  and  Bryozoa  (Davenport,  ’91,  et  al.)  and  among 
plants  (Goebel,  ’00).  Of  the  colony  form  of  the  tunicates 
Herdman  (’04,  p.  82)  says: 

The  marked  differences  in  the  appearance  of  the  colonies  of  compound 
Aseidians  is  largely  due  to  the  methods  of  budding;  even  in  those  of 
stolon  type  where  the  budding  is  practically  the  same  in  essential  nature, 
the  results  may  be  different  in  superficial  appearance,  according  as  the 
buds  are  formed  on  a short  stolon  close  to  the  parent  body,  or  from  the 
extremity  of  the  post  abdomen  or  from  the  long  epicardiae  tube  which 
may  extend  for  some  inches  from  the  ascidiozooid. 

Thus  we  conclude  that  the  innate  causes  of  different 
growth-forms  (colony  forms)  of  colonial  organisms  are 
(a)  the  m,ode  of  division  of  the  zooids  or  vegetative 
regions,  ( b ) the  ratio  of  stem  elongation  to  number  of 
zooids  or  buds  produced  or  uniformity  or  lack  of  uni- 
formity of  stem  elongation  (Wood-Jones,  p.  76)  closely 
related  to  (c)  the  presence  or  absence,  number,  position 
and  region  of  influence  of  the  dominant  growing  regions 
or  dominant  zooids,  and  ( d ),  in  some  cases,  the  grand 
period  of  growth  and  the  length  period  of  the  internodes 
(Johnson,  ’ll).  The  innate  tendencies  are  thus  reducible 
to  a few  principles  applicable  to  both  plants  and  animals. 

( c ) Responses  of  Motile  Organisms 

i.  Movements. — In  motile  organisms  the  most  striking 
responses  are  changes  in  position  brought  about  by 
movements  usually  more  or  less  random,  and  which  bring 
the  organism  into  various  conditions  one  of  which  usually 
relieves  the  disturbance.  The  organism  resumes  normal 
activity  in  conditions  which  brought  the  relief  (Jennings, 
’06).  These  conditions  are  not  necessarily  advantageous, 
but  are  usually  so  when  the  stimuli  are  those  encountered 
in  nature  (Mast,  ’ll).  Behavior  of  motile  organisms  is 
also  modified  by  repetition  of  action  even  in  animals  as 
low  in  the  animal  series  as  the  Protozoa  (Holmes,  ’ll). 


650 


THE  AMERICAN  NATURALIST  [ Vol.  XLVIII 


Jennings  (‘06)  has  quoted  various  botanical  workers ’ 
observations  on  motile  plants  the  behavior  of  which  prob- 
ably follows  the  general  laws  governing  the  behavior  of 
motile  animals.  As  a result  of  the  quick  behavior  re- 
sponses of  motile  organisms,  their  distribution  at  any 
given  time  is  a better  index  of  the  conditions  at  that  time 
than  the  distribution  of  sessile  organisms,  because  when 
the  conditions  at  a given  point  become  unfavorable  the 
motile  organisms  usually  move  to  another  situation, 
while  the  sessile  forms  remain  and  perhaps  die. 

ii.  Structural  Responses . — Among  motile  animals, 
structural  and  color  changes  occurring  as  a response  to 
environmental  conditions  (stimuli)  are  usually  not  of 
importance  to  the  organism  concerned.  The  color  differ- 
ences induced  in  Lepidoptera  by  heat  and  cold  (Stanfuss ; 
Fischer)  and  the  structural  differences  in  Crustacea  such 
as  were  brought  about  in  Cladocera  by  Woltereck,  and 
other  modifications  brought  forward  recently,  are  usually 
of  no  known  advantage  or  disadvantage  to  the  animals 
concerned  (Bateson,  ’13,  Ch.  IX  and  X).  Such  re- 
sponses in  color  and  general  form  do  not  ordinarily  take 
place  in  adults  subjected  to  such  conditions.  The  strik- 
ing structural  responses  of  motile  animals  are  often 
responses  to  the  organism’s  activity.  The  use  and  disuse 
phenomena  of  the  Lamarckians,  the  increase  in  size  and 
form  of  muscles,  thickening  of  skin  in  man  and  mammals, 
are  well-known  examples  of  a type  of  responses  which 
have  influenced  zoological  speculation.  Child  ( ’04)  con- 
trolled the  form  of  Leptoplana  by  controlling  activity. 
Holmes  (’07)  found  that  the  movements  of  pieces  of 
Loxophyllum  have  an  important  part  in  shaping  the 
general  outline  of  the  bodies  of  the  resulting  forms.  The 
general  forms  of  motile  animals  are  correlated  with  their 
activities  but  whether  form  or  structure  correlated  with 
it  appeared  first  in  the  course  of  evolution  has  been  the 
subject  of  considerable  fruitless  speculation. 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


651 


( d ) Responses  of  Sessile  Organisms 

i.  Structural  Responses . — The  striking  phases  of  re- 
sponses among  colonial  sessile  organisms  are  often 
changes  in  form  and  structure,  or  the  relative  position 
of  the  parts.  The  changes  in  structure  or  position  of 
parts  are  not  necessarily  advantageous  or  useful,  hut  are 
usually  so  when  the  stimuli  are  those  commonly  encoun- 
tered in  nature  (Cowles,  ’ll;  Loeb,  ’06,  p.  124;  Wood- 
Jones,  ’ll;  Ch.  VIII).  Indifferent  and  detrimental  re- 
sponses are  often  given  under  experimental  conditions  an! 
no  doubt  the  absence  of  such  variants  among  sessile  ani- 
mals collected  in  a wild  state  is  due  in  part  to  the  failure 
of  such  organisms  to  survive.  A few  sessile  colonial 
organisms  such  as  cacti  (Cowles,  ’ll)  show  little  or  no 
plasticity. 

Among  sessile  animals,  the  observations  of  Wood- 
Jones  form  the  best  examples  of  response.  He  found 
that  the  branching  type  of  corals  dominated  in  barrier 
pools,  tall  slender  non-branching  types  in  deep  water, 
and  massive  boulder  types  on  surf  beaten  shores.  Thus 
he  figures  similar  colonies  of  each  of  three  genera  which, 
while  possessing  certain  peculiarities  of  their  own,  are  in 
general  agreement  as  to  growth  form  just  as  sessile 
plants  usually  are ; and  this  in  part  for  comparable  rea- 
sons. Thus  various  conifers  occur  as  Krummholz  in  the 
high  mountains,  due  to  severe  conditions  (Cowles,  ’ll, 
p.  732),  wind,  snow,  and  in  part  to  the  injury  of  terminal 
growth  regions  of  the  main  stem  which  gives  rise  to 
lateral  branches.  The  boulder-like  corals  with  the  zooid 
at  the  same  level  occurring  on  the  surf-beaten  shores  of 
coral  islands  are  due,  in  the  case  of  Madrepora,  for  ex- 
ample, to  repeated  injury  of  the  terminal  dominant  zooids . 
Conifers  in  protected  situations  often  grow  into  tall 
slender  trees  comparable  with  the  (deep)  still-ivater 
corals.  The  barrier  pools  afford  conditions  where  the 
terminal  buds  are  less  often  injured  than  in  the  surf  and 
the  tree-like  branching  corals  result  from  minor  injuries 
to  dominant  zooids. 


652 


THE  AMEBIC  AN  NATURALIST  [Vol.XLVIII 


Wood- Jones  finds  further  that  still-water  corals  are 
less  strongly  calcified  than  those  in  rough  water,  the 
strains  producing  increased  secretion  analogous  to  in- 
creased tissue  production  as  a result  of  mechanical 
strains  in  plants  (Cowles,  p.  669).  Corals  show  different 
kinds  of  growth  under  different  environments  partic- 
ularly when  injured.  The  new  part  may  he  different 
from  the  rest  and  adjusted  to  the  environment  thus 
making  it  appear  as  though  two  “species”  occurred  in 
the  same  colony.  The  mode  of  division  of  the  zooid  is 
also  different  under  different  conditions.  Plants  show 
similar  variation  with  changes  of  conditions,  particularly 
in  the  leaves  which  are  divided  in  submerged  portions  of 
amphibious  plants  and  entire  in  the  emerging  portions 
(Cowles,  ’ll,  p.  595). 

As  has  been  noted,  there  is  nothing  in  sessile  animals 
that  is  more  than  roughly  analogous  to  leaves.  Leaves 
show  marked  structural  differences  on  different  parts  of 
the  same  tree  where  the  environmental  conditions  are 
different,  as,  for  example,  in  the  differences  which  occur 
between  the  upper  and  lower  portions  of  a forest  tree. 
While  there  are,  no  doubt,  differences  in  similar  details 
(histology)  in  the  organs  of  display  in  different  parts 
of  the  same  colony  of  sessile  animals,  little  or  nothing 
has  been  done  upon  them.  As  a further  indication  of  the 
prevalence  of  structural  response  in  sessile  organisms 
of  the  hydroids  Hickson  states  that  there  is  probably  but 
one  species  of  Millepora  which  occurs  in  a large  number 
of  growth  forms.  The  commercial  sponges  (Moore,  ’08) 
and  common  freshwater  sponges  and  polyzoa  show  many 
different  forms  under  different  environmental  conditions. 

The  major  differences  in  growth  form  induced  by  ex- 
ternal stimuli  in  colonial  organisms  result  from  modifica- 
tions of  the  rate  and  character  of  growth  with  respect  to 
the  four  innate  tendencies  toward  various  growth  or 
colony  forms  discussed  above,  and  which  may  be  briefly 
enumerated  as  follows:  (a)  mode  of  division,  ( b ) amount 
of  stem  elongation,  ( c ) influence  of  dominant  regions  and 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS  653 

(d)  grand  period  of  growth  and  the  length  of  period  of 
internodes. 

The  principles  are  concerned  with  asexual  reproduction 
and  apply  to  motile  organisms  only  exceptionally  as  for 
example  in  the  case  of  colonial  pelagic  forms.  The  laws 
are  applicable  to  both  plants  and  animals. 

ii.  Movements. — Movements  of  sessile  animals  are 
usually  contractions  or  extensions  of  parts  or  of  the 
entire  body.  Tentacles  and  comparable  organs  are  capa- 
ble of  movements  for  securing  prey.  Such  organs  often 
tend  to  wrap  about  objects  which  are  in  motion.  Many 
sessile  animals  are  capable  of  opening  and  closing  a 
mouth  opening  and  of  bending  or  twisting  the  entire  body. 
Plants  possess  a comparable  capacity  only  occasionally. 

(e)  Behavior  of  Sessile  Motile  Organisms 
Most  sessile  animals  are  capable  of  some  movement 
and  react  by  contraction  of  parts.  The  reactions  may  be 
modified  by  repeated  stimulation  (Jennings,  ’06)  and 
usually  by  physical  factors.  Some  animals,  as  Hydra , 
Stentor  and  many  others  are  both  sessile  and  vagile  or 
free-swimming,  and  show  different  types  of  behavior 
when  attached  and  when  free.  Jennings  states  that  such 
protozoa  have  a more  complex  behavior  than  motile 
forms.  This  is  due  to  their  combining  the  types  of 
behavior  of  sessile  and  motile  animals. 

(/)  j Response  and  Taxonomy  of  Sessile  Organisms 
Hickson  (’98)  has  stated  that  there  is  but  one  species 
of  Millepore  and  believes  that  sex  organs  will  be  found 
to  be  the  best  taxonomic  characters.  Wood-Jones  states 
that  there  are  far  fewer  species  of  corals  than  has 
formerly  been  supposed,  and  states  further  that  growth 
form  can  not  be  used  to  distinguish  species.  Among 
fresh-water  sponges  and  Bryozoa  reproductive  bodies 
(gemmules  and  statoblasts)  have  been  found  to  possess 
satisfactory  taxonomic  characters.  This  is  a situation 
quite  parallel  with  that  in  plants  where  reproductive 


654 


THE  AMERICAN  NATURALIST  [Vol.  XLYIII 


organs  are  used  as  classification  characters.  The  ideas 
of  the  reproductive  organs  of  plants  are  now  at  the 
“fixity’ ’ stage  which  on  the  animal  side  is  paralleled  by 
the  idea  of  fixed  tropisms  and  fixed  instincts,  of  a few 
years  since.  Variability  of  tropisms  is  now  well  recog- 
nized and  reproductive  organs  in  plants  are  being  found 
plastic,  as  those  of  animals  will  probably  be  found  also. 


III.  PARALLELISM  BETWEEN  SESSILE  AND  MOTILE  ORGAN- 
ISMS WITH  REFERENCE  TO  ECOLOGY 

From  a summary  of  the  considerations  above  it  will 
be  seen  that  for  practical  comparison  the  division  of 
organisms  into  plants  and  animals  may  be  abandoned  and 
only  reference  to  sessile  and  motile  organisms  made.  We 
may  now  turn  to  a discussion  of  a few  general  principles 
making  the  division  into  sessile  and  motile  organisms  only. 
The  behavior  of  motile  organisms  is  plastic.  There 
are  innumerable  cases  of  modification  of  reaction  by 
variations  of  physical  factors  (Jennings,  ’06;  Loeb,  ’06; 
Mast,  ’ll).  If  for  purposes  of  discussion  we  put  the 
usual  “normal”  reactions  of  motile  animals  over  against 
“normal”  structure  of  sessile  animals,  we  note  that  the 
behavior  response  of  the  former  parallels  the  structural 
response  of  the  latter. 

1.  Breeding 


Motile  Organism 

(a)  The  breeding  activities  take 
place  within  narrower  limits  than 
any  other  activities.  Merriam, 
*90;  Herrick,  ’02;  Reighard,  *08; 
Shelford,  Ala,  b,  c,  ’12 a,  b. 

( b ) The  selection  of  breeding 
place  and  breeding  activities,  in- 
cluding first  activities  of  the 
young,  are  governed  by  the  same 
general  laws  as  other  activities. 


Fixed  ( Sessile ) Organisms 

(a)  Breeding  and  other  activi- 
ties within  same  limits,  except  that 
dispersal  may  take  place  over  wide 
areas  through  detachability  of 
seeds  and  other  reproductive  bod- 
ies. 

(b)  Less  marked  because  a se- 
lection of  abode  by  sessile  organ- 
isms takes  place  through  the  be- 
havior of  motile  young  stages  or 
through  wide  dissemination  of  non- 
motile  bodies  by  wind  (etc.)  with 
growth  under  favorable  conditions 
and  failure  elsewhere. 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


655 


(c)  The  breeding  activities  are  (c)  The  reproductive  organs 
probably  least  modifiable  and  least  and  early  embryonic  stages  are 
regulatory.  less  modifiable  than  the  vegetative 

parts. 

( a , b,  c)  The  maple  tree,  a sessile  organism,  is  entirely 
stationary  in  its  adnlt  stages.  The  seeds  are  blown  by 
the  wind.  One  would  not  accomplish  much  in  the  study  of 
ecology  by  studying  the  distribution  of  the  seeds  of  the 
maple,  or,  on  the  other  hand,  by  the  study  of  the  distribu- 
tion of  adult  birds,  without  some  further  discrimination. 

Sessile  organisms  are  not  difficult  to  associate  with 
their  proper  environmental  conditions  in  their  adult 
stages.  As  we  proceed  in  our  study  to  forms  which  can 
move  readily  and  rapidly,  the  difficulty  of  associating 
them  with  their  definite  environmental  conditions  in- 
creases. Sessile  organisms  have  stages  which  are  small 
and  capable  of  easy  dispersal,  as  in  the  case  of  the  maple. 
Sessile  marine  animals  and  some  sessile  plants  frequently 
have  motile  forms  in  young  stages.  In  these  motile 
stages  they  are  governed  by  the  same  laws  as  other  motile 
organisms.  The  conditions  under  which  the  motile  stages 
develop  into  the  sessile  forms  are  crucial. 

Most  fresh-water  forms  and  some  marine  forms  of 
sessile  organisms  are  without  the  free-swimming  stage, 
and  they  produce  non-motile  stages  physiologically 
comparable  to  the  seeds  of  higher  plants.  The  winter 
bodies  (statoblasts)  of  the  Bryozoan  ( Pectinatella ) com- 
mon near  Chicago,  and  which  is  a strictly  sessile  organ- 
ism, are  comparable  to  seeds  and  probably  require 
“ripening”  by  cold,  just  as  do  many  seeds  and  the  repro- 
ductive bodies  of  some  other  species  of  the  same  group. 
Organisms  which  are  highly  motile  in  the  adult  stages 
are  not  motile  in  the  egg  and  young  stages.  The  eggs 
and  young  of  birds,  for  example,  do  not  move  about,  yet 
birds  are  the  most  motile  of  all  animals. 

2.  Comparison  of  the  Sessile  and  Motile  Elements  of 

the  Biota 

(a)  The  motile  organisms  of  a (a)  The  sessile  organisms  of  a 
given  habitat  usually  react  simi-  given  habitat  (particularly  plants) 


656 


THE  AMEBIC  AN  NATURALIST  [Vol.  XLYII1 


larly  to  two  or  more  stimuli  not 
differing  greatly  in  intensity  from 
their  optimum,  i.  e.,  the  percent- 
age of  positive  or  negative  trials  is 
essentially  the  same  for  standard 
intensities.  There  is  also  probably . 
similarity  in  the  rates  of  metabol- 
ism, etc. 

( b ) The  specificities  of  behavior 
such  as  the  mode  of  moving  the 
organs,  e . g.,  of  locomotion,  and 
in  some  cases  the  combined  results 
of  different  behavior  reactions  are 
similar  and  hence  are  ecologically 
equivalent.  The  size  and  efficiency 
of  the  organs  are  also  involved. 


usually  show  similar  functional 
rates,  such  as  similar  rates  of 
transpiration  among  sand  dune 
plants. 


(b)  The  various  structural  de- 
vices which  meet  the  conditions  of 
the  environment  are  ecologically 
equivalent. 


A testing,  for  example,  of  the  rheotaxis  of  a large  num- 
ber of  brook-rapids  animals  has  shown  them  to  he 
strongly  positive,  and  when  active  individuals  only  are 
considered  the  percentage  of  positive  trials  is  very 
similar  for  the  entire  rapids  community.  Likewise  they 
are  in  accord  in  their  avoidance  of  sand  bottom.  Many 
of  the  animals  have  special  means  of  attachment  which 
may  be  brought  into  play  with  speed. 

As  has  already  been  pointed  out  elsewhere,  ecological 
equivalence  is  illustrated  here.  The  darters  (fish)  are 
strong  swimmers  and  are  able  to  live  in  rapids  by  virtue 
of  their  swimming  powers  and  positive  reaction,  while 
snails  meet  the  same  general  conditions  through  positive 
rheotaxis  and  the  strong  foot  which  enables  them  to  hold 
to  rocks. 


3.  Sessile  and  Motile  Okganisms  in  Ecological 
Succession 

(a)  Ecological  succession  is  succession  of  ecological 
(physiological)  types  over  a given  area,  due  to  changes  of 
conditions  which  both  cause  migration  of  physiological 
types  and  transformation  of  such  types  as  remain  (Shel- 
ford,  ’11a,  ’ll b,  ’ll d,  ’12 a,  ’12fr  and  citations).  Changes 
of  conditions  are  geographic,  i.  e.,  physiographic,  climatic, 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


657 


etc.,  and  biological  (due  to  organisms).  Sessile  plants 
are  the  chief  biological  cause  of  succession  on  land  and 
in  fresh  water,  while  sessile  animals  are  the  chief  biolog- 
ical cause  in  the  shallow  portions  of  the  sea,  especially  in 
coral  reef  regions  (Wood- Jones,  ’ll).  Sessile  organisms 
are  more  important  causes  of  succession  than  motile  ones 
because  they  (a)  build  up  the  substratum  with  detritus 
and  skeletons,  (b)  interfere  with  the  movement  of  the 
surrounding  medium,  (c)  cut  off  light  from  the  sub- 
stratum where  other  organisms  must  reside  and  their 
own  young  secure  foothold,  and  ( d ) they  usually  affect 
their  own  environments  with  excretory  products  more 
than  do  motile  organisms.  In  general  we  recognize 
ecological  succession  of  motile  animals  through  the  differ- 
ences of  behavior  which  accompany  changes  in  conditions. 
The  differences  are  physiological ; differences  in  behavior 
are  the  easiest  index  of  the  physiological  condition.  The 
character  of  nests,  burrows,  etc.,  are  often  good  indi- 
cators also. 

IV.  INFLUENCE  OF  RESPONSE  PHENOMENA  UPON  BIOLOGICAL 
THEORY  AND  CONTROVERSY 

A glance  at  some  aspects  of  biological  speculation 
since  before  the  publication  of  Darwin’s  “Origin  of 
Species”  is  essential  to  our  understanding  of  the  atti- 
tude of  biologists  until  recently,  toward  responses. 

1.  Teleological  View 

In  the  matter  of  animal  behavior  response,  the  earlier 
workers  interpreted  the  reactions  as  intelligent  and  pur- 
poseful, ascribing  human  sensations,  etc.,  to  animals  as 
low  in  the  scale  as  protozoa.  This  teleological  tendency 
was  paralleled  on  the  plant  side  by  the  idea  of  purposeful 
adaptive  responses.  Many  common  plants  respond 
(structurally)  readily  to  environmental  conditions.  As 
has  been  noted,  the  commonest  of  the  surviving  responses 
of  the  wild  state  are  apparently  advantageous.  This  led 
some  botanists  to  a Lamarckian  teleological  conception  of 
response,  perhaps  best  represented  by  Kerner  and 


658  THE  AMEBIC  AN  NATURALIST  [Vol.  XLYIII 

Oliver’s  work  on  the  natural  history  of  plants.  Accord- 
ing to  this  view,  responses  are  advantageous  and  for  the 
purpose  of  preserving  the  plant.  Thus  response  and 
adaptation  become  synonymous  (Coulter,  ’08),  a usage 
quite  inapplicable  to  animal  structure.  At  the  beginning 
of  the  recognition  of  the  response  phenomena  of  corals 
Wood-Jones  takes  essentially  the  view  of  adaptation 
which  botanists  have  tried  and  rejected. 

Lamarck,  who  was  for  many  years  engaged  in  botanical 
work,  must  have  noted  many  cases  of  advantageous 
structural  response  in  plants.  Later  he  undertook  the 
study  of  invertebrates  which  show  great  plasticity,  and 
was  naturally  much  influenced  in  the  development  of  his 
theory  of  transmutation  of  species  by  the  response  phe- 
nomena in  the  plastic  organisms  which  he  studied.  Thus 
the  responses  of  motile  (as  well  as  sessile)  organisms 
which  result  from  their  own  activities  or  the  action  of 
their  environments  formed  an  important  feature  of 
Lamarck’s  (Packard,  ’01;  Cope,  ’96)  theory  of  transmu- 
tation of  animal  species.  His  theory  is  clearly  in  accord 
with  the  material  he  studied  most.  * The  nature  of  his 
contention  and  various  well-known  circumstances  caused 
his  ideas  not  to  be  accepted. 

2.  Natukal  Selection  View 

Characters  used  in  classification  of  motile  animals 
before  and  since  the  time  of  Darwin  are  quite  frequently 
adaptation  characters.  Thus  the  large  pectoral  fins  and 
absence  of  an  air  bladder  are  characteristics  of  an  entire 
group  of  fishes,  the  darters.  The  divided  eyes  of  the 
Gyrinidce,  which  swim  at  the  surface  of  the  water,  are  so 
adjusted  that  one  half  looks  downward  into  the  water, 
and  the  other  outward  into  the  air.  This  character  com- 
bined with  the  paddle-like  hind  legs  would  have  served  to 
distinguish  the  family.  Again  larvae  with  a head  and 
thorax  modified  to  fit  a circular  burrow  and  with  hooks  on 
the  dorsal  surface  of  the  fifth  abdominal  segment,  which 
is  supposed  to  be  an  adaptation  to  prevent  the  animals 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


659 


from  being  drawn  from  their  cylindrical  burrows  by 
their  prey,  could  serve  to  distinguish  the  entire  family  of 
Cicindelidce  (tiger  beetles).  Such  cases  might  be  multi- 
plied indefinitely. 

Following  Lamarck  came  Darwin,  who,  being  more  par- 
ticularly a zoologist,  was  probably  (proportionately,  at 
least)  less  familiar  with  structural  response  phenomena. 
He  was  apparently  impressed  with  the  “fixity’ ’ of  the 
so-called  adaptation  characters  in  motile  animals,  and 
with  the  fact  that  they  are  often  family,  generic  or  specific 
characters.  With  the  assumption  that  they  originated  in 
the  environment  in  which  they  are  now  found,  Darwin 
and  his  followers  on  the  zoological  side  credited  “natural 
selection”  of  structural  characters  with  the  origin  of 
species.  Though  broader  than  Lamarck,  this  important 
feature  of  Darwin’s  theory  was  quite  clearly  drawn  from 
data  on  motile  animals.  After  the  acceptance  of  Darwin’s 
theory,  biologists  were  for  many  years  engaged  in  elabo- 
rating the  ideas  of  phylogeny  and  natural  selection  by 
working  out  recapitulations  and  homologies  and  by  point- 
ing out  cases  of  adaptation.  The  investigation  was 
largely  confined  to  the  highly  individuated  animals.  The 
morphological  method  of  this  period,  which  indeed  has 
still  continued  in  use  among  a minority  of  zoologists  and 
which  finds  a parallel  in  the  recent  morphological  study 
of  the  sex  organs  of  plants,  belongs  to  descriptive  rather 
than  to  analytical  science.  Since  its  conclusions  are  often 
based  upon  the  arrangement  of  species  or  of  stages  in 
development  into  series  chosen  by  the  investigator,  it  is  a 
method  which  often  allows  free  play  of  subjective  fancy. 
Thus  unconsciously  experimental  study  of  modification  by 
environment  became  more  and  more  neglected,  and  the 
dominant  type  of  investigation  being  such  as  to  show 
only  the  usual  course  of  events  in  development,  the  ideas 
of  fixity  grew  more  and  more.  Thus  the  fact  that  the 
external  form,  structure  and  color  of  animals  are  not 
easily  modified  without  careful  experimental  methods, 
and  that  the  structural  responses  of  sessile  animals  were 


660 


THE  AMERICAN  NATURALIST  [Vol.  XLYIII 


so  little  known,  resulted  in  structure  in  animals  being  fre- 
quently regarded  as  fixed  and  every  resemblance  and 
peculiarity  being  too  often  regarded  as  significant.  The 
explanations  of  supposed  adaptations  among  animals  fell 
largely  to  the  theory  of  natural  selection  which  was 
strained  by  some  (see,  for  example,  in  Romanes,  ’92,  p. 
269)  to  explain  origins  in  great  detail,  largely  on  the  basis 
of  the  competition  of  species  for  food,  etc.  Explanations 
along  this  line  were  carried  to  a reductio  ad  absurdum  as 
indicated  by  Livingston  ( ’13)  and  have  by  no  means  dis- 
appeared from  the  scientific  calendar.  This  tendency 
was  less  important  on  the  plant  side.  More  attention  was 
given  to  speculation  concerning  adaptive  response. 

From  a consideration  of  the  facts  just  presented,  we 
note  that  the  characters  of  the  two  leading  early  view 
points  in  evolution  were  no  doubt  influenced  if  not  actually 
caused  to  crystallize  into  their  peculiar  form  by  the  failure 
of  workers  to  recognize  the  entire  series  of  phenomena 
which  we  have  presented  above.  Thus  a review  of  the 
responses  of  sessile  and  motile  organisms  throws  much 
light  on  the  influences  leading  to  the  first  conceptions  and 
later  modification  of  these  two  leading  doctrines.  Botan- 
ists for  many  years  dwelt  mainly  on  the  response  of  sessile 
organisms  and  crystallized  a Lamarckian  conception  of  the 
origin  of  adaptations  through  the  fixing  of  advantageous 
responses  as  hereditary  characters.  During  the  same 
period  zoologists  essentially  ignored  sessile  and  other 
multiple  individualed  animals  and  their  great  plasticity 
and  crystallized  the  Darwinian  idea  into  Weismannian 
germplasm  doctrine  based  on  highly  specialized  single 
individualed  animals. 

3.  Supposed  Non-Inheritance  of  Response  and  the 
Germ  Plasm  Doctrine 

The  theory  of  the  independence  of  the  germ-plasm  from 
the  soma,  and  its  continuity  from  generation  to  genera- 
tion, was  brought  strongly  to  the  attention  of  zoologists 
in  1885  by  Weismann.  It  was  the  natural  outgrowth  of 
the  methods  and  theories  of  the  preceding  period  and 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


651 


was  largely  based  upon  the  non-inheritance  of  mutila- 
tions and  the  fact  that  the  germ  cells  of  a few  organisms 
are,  morphologically,  early  differentiated  from  the  soma. 
Turning  to  its  influence  upon  ideas  concerning  response, 
we  note  that  from  this  viewpoint  details  of  structure 
were  not  of  fundamental  importance  unless  traceable  to 
the  germ  plasm.  Still,  structural  details  were  more  im- 
portant than  response,  because,  with  the  exception  of 
instincts,  responses  were  believed  to  occur  independently 
of  the  germ  plasm  and  hence  were  of  interest  only  on 
their  own  account.  Thus  the  methods  used  in  applying 
Darwin’s  theory  led  to  neglect  of  experimental  study  of 
response  and  culminated  in  the  extreme  views  of  Weis- 
mann.  The  germ-plasm  theory  or  the  ideas  of  heredity 
which  are  associated  with  it  has  dominated  zoological 
thought  almost  if  not  quite  down  to  the  present  day.2 

4.  The  Influence  of  the  Study  of  Response  on 
Peesent-Day  Biological  Theoey 

One  of  the  most  striking  developments  of  recent  years 
has  been  the  discovery  that  behavior  responses  are  modi- 
fiable to  a high  degree.  Small  traces  of  reagents  reverse 

2 Unconsciously  suggestions  of  the  supernatural  which  come  up  in  connec- 
tion with  heredity  and  evolution  have  stimulated  investigators  to  study  and 
speculation,  though  they  have  often  approached  the  question  of  heredity  with 
an  unscientific  attitude.  This  is  indicated  by  such  statements  as  “I  could 
not,  however,  resist  the  temptation  to  endeavor  to  penetrate  the  mystery  ->f 
this  most  marvelous  and  complex  chapter  of  life”  and  ‘‘the  momentous 
issues  involved”  and  “no  more  fundamental  problem  could  well  be 
stated”  bear  out  this  statement.  The  ardency  which  appears  here  and 
elsewhere  in  the  discussion  of  scientific  questions,  appears  to  the  writer  to 
be  associated  with  the  discussion  of  problems  which  can  not  be  referred 
to  existing  facts  for  solution.  Few  of  the  present  generation  of  scientific 
men  acquired  a working  knowledge  of  the  methods  of  science  before  the 
age  of  twenty-five  years,  and  the  early  habits  of  mind  were  formed  in  the 
atmosphere  of  the  supernatural  and  dogmatic,  which  has  characterized 
human  thought  for  centuries.  It  is  doubtful  if  the  majority  of  us  can 
maintain  a scientific  attitude  for  more  than  a short  period;  we  must  con- 
stantly come  back  to  our  tests  and  principles.  This  may  account  for  many 
of  the  contradictions  regarding  scientific  principles  which  one  finds  in  the 
conversation  of  scientific  men.  When  the  methods  of  science  have  become 
the  methods  of  society  we  may  expect  a group  of  scientific  men  far  more 
effective  than  we  ourselves  can  hope  to  be. 


662 


THE  AMERICAN  NATURALIST  [Vol.XLVIII 


reactions.  Intelligent  behavior  occurs  in  the  lower* 
Arthropods.  Even  Paramoecium  shortens  the  time  re- 
quired to  turn  around  in  a tube,  by  repetition.  Actions 
formerly  regarded  as  instinctive  now  appear  to  be  mere 
innate  tendencies  perfected  by  repetition.  Thus  the  ideas 
of  fixity  have  essentially  disappeared  from  this  field. 

The  response  of  organisms  to  injuries  and  the  general 
control  of  form  in  the  lower  groups  has  done  much  to 
break  down  the  ideas  of  fixity  developed  by  Weismann 
and  embryological  schools.  Thus  Child,  the  leading 
American  worker  in  this  line,  is  able  to  control 
size,  form,  number  of  eyes  in  the  case  of  Planarians. 
Various  writers  have,  found  modifications  inherited  after 
several  generations  of  repeated  stimulation  (see  Bateson, 
’13).  The  development  of  anti-bodies  (immunity)  has 
been  shown  to  be  a response  occurring  in  connection  with 
many  normal  processes.  The  discovery  of  responses  of 
so  many  types  has  led  to  abandoning  ideas  of  fixity  even 
among  students  of  embryology  and  genetics.  Thus  we 
note  the  recent  decline  of  the  doctrine  of  continuity  and 
independence  of  the  germ  plasm  and  kindred  doctrines 
and  points  of  view,  which  constitute  the  central  ideas  of 
fixity.  It  will  accordingly  be  profitable  to  consider  some 
further  facts  which  make  the  germ-plasm  doctrine  un- 
necessary. 

5.  Aspects  of  the  Unten  ability  of  the  (term 
Plasm  Doctrine 

The  presence  of  primordial  germ  plasm  is  assumed 
even  in  sessile  colonial  organisms  such  as  plants,  coelen- 
terates,  and  in  flatworms,  etc.,  where  under  certain  con- 
ditions any  small  part  of  the  body  may  give  rise  to  a 
complete  organism.  Here  the  theory  is  not  needed  to 
explain  the  facts. 

Child  (’ll)  said: 

The  theory  of  the  continuity  of  the  germ  plasm  as  a system,  inde- 
pendent of  the  soma,  except  as  regards  nutrition,  has  played  an  im- 
portant part  in  biological  thought  during  the  last  two  decades,  but  I 
am  convinced  that  it  has  led  in  the  wrong  direction  and  that  it  is  re- 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


663 


sponsible  for  many  pseudo-problems  of  heredity  and  development, 
which  on  the  basis  of  a different  theory  could  never  have  occupied  the 
attention  and  wasted  the  energy  of  biologists.  Briefly  my  position  is, 
that  the  gonad  primordium  is,  at  least  up  to  a certain  stage  of  develop- 
ment, physiologically  a part  of  the  individuality  as  are  other  organs, 
and  that  its  further  history  of  differentiation  into  male  and  female 
gametes  indicates  that  it  becomes  specified  in  a particular  direction,  at 
least  partly  in  consequence  of  its  correlative  environment  in  the  or- 
ganism. 

The  independence  of  the  germ  plasm  is  not  well  sup- 
ported physiologically.  Thus  Wilson  (T2,  p.  163)  says 
of  the  effect  of  prolonged  ingestion  of  alkaline  salts  by 
mice: 

No  obvious  changes  were  evident  in  the  liver,  kidneys,  lungs,  spleen 
and  intestines  but  in  the  testes  some  extraordinary  alterations  were 
found.  These  results  are  of  especial  interest  because  as  the  cells  of  the 
testes  except  the  basal  cells  are  regarded  by  many  cytologists  as  out  of 
coordination  with  the  somatic  cells.  As  a result  of  these  experiments 
it  would  seem  that  they  are  more  susceptible  to  changes  in  reactivity 
than  the  surrounding  plasma. 

Dungay  (’13)  and  authors  cited  have  thrown  compara- 
ble light  on  this  question. 

The  facts  of  embryology  themselves  are  but  a pseudo 
argument  in  its  favor.  The  organisms  in  which  continu- 
ity is  supposedly  demonstrable  are  highly  individuated 
and  their  organs  highly  specialized  and  many  different 
organs  are  early  separated  from  the  common  mass  of 
cells.  The  germ  cells  thus  follow  the  general  law  of 
development  in  such  animals.  The  germ  plasm  is  prob- 
ably no  more  independent  of  other  parts  of  the  organism 
than  is  the  liver  or  any  other  special  tissue.  “Germ 
plasm”  and  “germinal  continuity,”  if  such  exist,  may 
thus  be  merely  incidental  to  the  particular  type  of  organi- 
zation of  the  specialized  individuals  in  which  they  occur. 

It  should  further  be  noted  that  on  the  botanical  side 
this  doctrine  of  the  independence  and  continuity  of  the 
germ  plasm  has  received  little  attention  and  has  been 
given  little  credence  because  “germ  plasm”  arises  from 
different  tissues  and  is  neither  set  aside  early  from  the 
soma  nor  is  it  in  any  other  sense  clearly  continuous. 


664 


THE  AMERICAN  NATURALIST  [Vol.  XLVI1I 


Furthermore,  the  plasticity  of  plant  structures  made  the 
application  of  the  doctrine  of  natural  selection  to  sup- 
posed adaptations  untenable,  and  this  type  of  explanation 
has  received  little  more  attention  with  botanists  than  have 
Lamarckian  speculations  with  zoologists.  The  adaptation 
characters  of  plants  can  not  ordinarily  be  used  as  taxo- 
nomic criteria  (Coulter,  ’08). 

6.  The  Measure  of  Values  in  Biological  Science 

One  hears  reference  to  pure  science  as  something  quite 
apart  from  applied  science.  It  is  indeed  true  that  inves- 
tigators in  pure  science  are  to  some  degree  prompted  to 
push  forward  in  research  by  interest  in  the  problems  for 
their  own  sakes.  But  the  human  mind  does  not  work  long 
isolated  from  practical  affairs  or  the  main  channels  of 
human  interest,  and  it  is  doubtful  if  the  pure-science 
investigator  continues  long  in  this  way.  Observations  are 
soon  connected  up  in  some  way,  actual  or  possible,  with 
some  human  interest,  be  it  as  remote  as  the  improving  of 
human  stock  in  remotely  future  generations.  Thus  “pure 
science”  defined  as  investigation  for  investigation’s  sake 
hardly  exists  so  far  *as  the  pure-science  workers  are 
concerned,  but  may  be  best  defined  as  an  indirect  method 
of  attacking  problems  of  general  importance.  It  differs 
from  applied  science  in  that  application  to  practical 
problems  is  not  its  aim,  though  the  estimated  value  of 
theories  and  results  in  “pure”  science  are  often  greatly 
modified  by  applicability  to  practical  questions. 

Certain  problems  and  groups  of  facts  in  biology  are 
sometimes  referred  to  as  fundamental.  Some  one  has 
said  that  a fundamental  problem  is  one  the  solution  of 
which  biologists  have  decided  will  give  greatest  progress. 
It  is  doubtless  true  that  a few  leaders  reach  such  decisions 
with  regard  to  particular  questions,  but  the  real  causes 
of  their  general  acceptance  as  fundamental  are  social 
and  imitative.  Thus  when  one  investigator  or  a small 
group  of  investigators  arrives  at  such  a decision  many 
others  usually  become  active  along  the  same  lines  largely 
because  it  is  a popular  topic.  Thus  under  the  influence 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


G65 


of  a group  of  investigators  among  whom  Weismann  was 
a conspicuous  leader,  problems  of  the  germ  cells,  the 
egg’s  early  development,  and  heredity,  became  “ funda- 
mental problems.”  They  evidently  argued  that  since  all 
comes  from  the  egg  and  germ  cell,  all  must  be  discover- 
able in  the  egg.  If  germ  plasm  were  as  independent  from 
soma,  as  completely  insulated  from  environment  as  con- 
tinuous from  generation  to  generation  as  has  been 
assumed,  the  study  of  germ  plasm  would  be  the  only  way 
to  the  solution  of  the  problems  of  heredity  and  evolution. 
This  follows  no  matter  whether  the  chromosomes  or 
almost  the  entire  egg  are  credited  with  carrying  heredi- 
tary qualities;  only  the  postulation  of  continuity  and 
independence  from  soma  and  insulation  from  environ- 
ment are  necessary.  If  the  independence  of  germ  plasm 
from  soma  be  accepted  even  in  a weakened  and  modified 
form  it  follows  that  studies  of  somatic  characters  can  at 
most  be  of  secondary  importance  from  the  point  of  view 
of  heredity  and  evolution.  Thus  in  some  quarters  the 
value  of  various  lines  of  zoological  work  has  been  esti- 
mated largely,  unconsciously,  no  doubt,  in  proportion  to 
the  nearness  or  remoteness  of  their  relation  to. the  “germ 
plasm”  question. 

Thus  it  is  true  that  in  biology  as  in  all  other  fields 
values  are  measured  consciously  or  unconsciously  by 
criteria.  In  recent  years  another  better  criterion  of  value 
has  made  its  appearance  among  zoologists.  The  germ 
plasm  criterion  already  discussed  was  primarily  morpho- 
logical; the  second  is  physiological,  borrowed  no  doubt 
from  physiologists.  It  measures  values  on  the  basis  of 
the  analysis  of  the  organisms  into  terms  of  physics  and 
chemistry  or  is  concerned  with  a mechanistic  conception 
of  life  in  all  its  manifestations.  From  this  viewpoint  the 
study  of  each  and  every  part  of  the  organism  is  important 
because  the  discovery  of  laws  governing  one  part  is 
usually  or  at  least  often  of  general  importance.  Investi- 
gations from  this  viewpoint  have  shown  that  the  germ 
plasm  criterion  is  clearly  illogical  in  its  application  to  the 
study  of  somatic  characters  because  it  is  based  upon  the 


666  THE  AMERICAN  NATURALIST  [Vol.XLVIII 

tacit  assumption  that  the  soma  is  governed  by  different 
laivs  from  the  living  matter  which  makes  up  the  germ 
plasm  from  which  it  arose.  In  other  words  it  is  assumed 
that  the  germ  plasm  is  so  different  from  the  soma  that 
the  discovery  of  laws  governing  the  soma  is  a type  of 
investigation  of  relatively  little  significance. 

Some  criterion  of  values  is  of  course  necessary  in  sci- 
ence as  well  as  elsewhere,  and  for  the  sake  of  argument  we 
would  be  willing  to  accept  the  second  when  broadly  stated 
and  the  first  when  broadened  and  modified  so  as  to  accord 
with  the  second  as  appears  to  be  the  case  among  certain 
students  of  genetics.  In  other  words,  problems  of  the 
germ  cells,  the  egg,  and  heredity,  are  of  much  importance 
when  the  germ  cells  themselves  are  regarded  as  dynamic 
and  in  their  relations  to  the  dynamics  of  the  organism 
as  a whole. 

Granting  that  these  are  true  and  tenable  criteria  of 
values  in  present-day  biological  science,  what  is  to  be  the 
method  of  application?  Should  biology  demand . that 
results  be  of  direct  application  to  these  “central”  prob- 
lems? One  has  but  to  look  at  the  history  of  almost  any 
branch  of  science  to  find  that  great,  if  not  the  greatest, 
advances  have  come  through  following  up  results  at 
points  where  relations  to  the  central  problems  of  the 
period  were  quite  unsuspected,  or  by  the  transference 
of  methods,  principles  and  results  from  one  field  to  an- 
other where  relations  between  the  two  were  not  suspected. 
Take,  for  example,  immunity  and  immunization,  the  his- 
tory of  which  is  ably  sketched  by  Adami  ( ’08,  pp.  451- 
528).  It  has  been  known  for  ages  that  one  attack  of  many 
infectious  diseases  yields  more  or  less  complete  immunity 
from  subsequent  attacks.  Thus  for  centuries  in  India 
and  the  East  individuals,  chiefly  children,  have  been  pur- 
posely inoculated  with  matter  or  by  contact.  The  prac- 
tise grew  out  of  experience  showing  that  diseases  thus 
communicated  to  healthy  individuals  from  weaker  ones 
are  less  severe.  In  1796  the  results  of  Jenner  on  vaccina- 
tion with  cowpox  were  published.  This  may  have  influ- 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


667 


enced  Pasteur,  who  over  eighty  years  later  laid  the 
foundation  for  the  modern  epoch  of  development,  by 
combating  a plague  of  diarrhoea  in  poultry  (1880). 
During  the  twenty  years  following,  various  investigators 
added  noteworthy  contributions,  and  about  1900  Ehrlich 
and  Morgenroth  evolved  the  “side-chain  theory ” by 
which  a large  number  of  possible  conditions  can  be  pre- 
dicted and  all  the  observed  facts  of  immunity  explained. 
While  not  expressed  in  strictly  chemical  terms,  the  theory 
and  the  experiments  which  support  it  are  very  important 
both  practically  and  theoretically.  In  recent  years  the 
knowledge  of  immunity  and  comparable  phenomena  have 
been  greatly  extended.  Various  workers  (Pfeifer,  Vol. 
II,  p.  262)  have  shown  similar  phenomena  in  the  .increased 
resistance  of  plants  to  poisons,  thus  making  the  responses 
of  plants  and  animals  still  more  generally  comparable. 
Most  recently  workers  on  problems  such  as  fertilization 
(Lillie,  ’13),  standing  in  close  relation  to  the  older  germ- 
plasm’  doctrine,  have  discovered  facts  belonging  to  this 
field  and  made  use  of  Ehrlich’s  theory  to  explain  the  ob- 
servations. This  development  has  helped  to  confirm  the 
conclusion  of  some  investigators  that  immunity  phe- 
nomena represent  important  features  of  the  chemical 
mechanism  of  life.  Adami  has  remarked, 

That  a plague  of  diarrhoea  in  a poultry  yard,  studied  by  a professor 
of  chemistry,  should  be  the  seed  from  which  has  grown  the  vast  de- 
velopment of  later  years  is  a strange  fact,  but  a fact  nevertheless. 

What  was  the  attitude  of  pure  science  so  called,  of 
germ-plasm  doctrinairies,  and  biologists  generally  during 
the  long  period  which  elapsed  before  they  could  make 
use  of  his  results?  CleaTly  it  was  one  of  indifference,  if 
not  disgust,  toward  the  subject.  The  probable  result  of 
such  attitudes  on  the  progress  of  the  investigation  of 
immunity  phenomena,  had  it  not  been  for  their  immense 
practical  significance,  is  clear.  They  could  not  have 
received  their  proper  share  of  attention.  Thus  in  the 
pursuit  of  the  analysis  of  the  chemical  mechanism  of  life 
men  who  sought  it  directly  have  failed  in  this  one  impor- 


668 


THE  AMEBIC  AN  NATURALIST  [ Vol.  XLYIII 


tant  step,  and  the  chief  contribution  has  come  from  very 
remote  indirect  methods.  Generally  speaking  the  inves- 
tigators who  choose  a direct  method  of  attack  often  put 
themselves  somewhat  in  the  position  of  the  chemist  who 
would  make  chemical  analysis  of  living  matter  when  his 
first  step  defeats  its  own  purpose  by  killing  the  substance 
to  be  analyzed.  The  failure  of  exclusively  direct  methods 
is  often  evident.  Still  the  ability  to  obtain  results  by  the 
method  of  direct  attack,  combined  with  a far  too  rare 
ability  to  tie  with  them  indirectly  obtained  data,  some- 
times gives  noteworthy  contributions. 

It  accordingly  remains  to  be  seriously  considered 
whether  or  not  biology  can  afford  to  apply  criteria  to  the 
measure  of  the  values  of  investigation.  Their  application 
is  of  course  largely  unconscious,  but  the  effects  are  not 
thereby  modified.  Noteworthy  results  of  their  applica- 
tion are  (a)  concentration  of  work  in  certain  lines  indi- 
cated by  a given  criterion,  and  ( b ) an  actual  abandoning 
to  a large  degree  of  remote  and  indirect  methods  of 
attacking  the  problems  which  the  criterion  involves.  This 
means  the  partial  abandoning  of  the  methods  for  which 
pure  science  stands. 

Criteria  can  be  safely  used  only  in  a very  broad  gen- 
eral way,  and  in  application  more  often  to  past  progress 
than  to  current  investigation.  They  are  perhaps  most 
valuable  as  a guide  to  individual  investigators  working 
on  problems  remote  from  these  more  or  less  central 
“pure  science”  questions.  That  some  guide  should  be 
in  the  hands  of  such  workers  is  beyond  question.  In  the 
hands  of  those  attacking  the  problems  directly  they  often 
appear  detrimental  because  they  soon  take  on  an  extreme 
form  and  become  regarded  as  fundamental.  At  this 
stage  they  are  usually  in  need  of  extensive  revision.  If 
the  investigator  is  contributing  observations  and  details 
only,  he  is  doing  a great  service,  for  such  information  is 
needed  everywhere.  If  he  is  able  to  combine  his  own  and 
others  results,  he  almost  invariably  draws  data  from  all 
sources,  direct  and  indirect , far  and  near.  Granted  the 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


669 


ability  to  synthesize,  the  opportunity  to  nse  the  ability 
sometimes  comes  to  those  who  attack  the  so-called  cen- 
tral problems  directly.  It  comes  equally  often  (we  believe 
more  often)  to  those  who  have  led  np  to  the  central  prob- 
lem from  some  remote  viewpoint,  frequently  condemned 
by  the  followers  of  direct  method  of  attack.  Granting 
the  importance  of  synthesis,  if  the  biologist  seeks  the 
solution  of  such  a problem  as  the  germ-plasm  problem, 
he  should  encourage  workers  to  start  at  points  as  remote 
from  the  subject  as  possible,  that  they  may  approach  it 
with  new  light  and  from  new  angles. 

In  judging  the  work  of  another,  its  value  should  be 
determined  more  by  the  (a)  strictness  of  scientific  method 
used,  (b)  the  thoroughness  and  completeness  of  the  in- 
vestigation, and  ( c ) (and  perhaps  most  important  of  all) 
evidence  of  ability  to  synthesize  and  combine  other  re- 
sults with  his  own  with  a view  to  broader  generalization. 
It  must,  however,  also  be  recognized  that  there  are  many 
biological  problems  of  much  human  importance,  which 
must  be  solved  quite  independently  of  the  ideal  central 
problems  of  pure  science. 

6.  Summary  and  Conclusions 

From  the  data  presented  above,  we  note  that  the  doc- 
trine of  purposeful,  advantageous  response  (including 
anthropomorphic  ideas)  arose  from  the  uncritical  non- 
experimental  study  of  the  responses  (structural)  of  ses- 
sile and  (behavior)  motile  animals.  The  idea  of  the  all- 
sufficiency  of  natural  selection  is  largely  the  outcome  of 
observational  study  of  apparently  fixed  and  yet  appar- 
ently adaptive  characters  of  motile  highly  individuated 
animals.  The  doctrine  of  the  continuity  of  the  germ 
plasm  is  likewise  the  outgrowth  of  the  study  of  highly 
individuated  animals  in  which  the  various  organs  are 
early  differentiated  in  the  dividing  egg.  No  one  of  the 
doctrines  is  wholly  tenable ; no  one  is  more  than  a partial 
truth.  Each  appears  to  have  arisen  from  a recognition 
of  certain  more  or  less  unconsciously  selected  and  un- 
critically interpreted  phenomena  by  each  of  several  men 


670 


THE  AMEBIC  AN  NATURALIST  [Vol.  XL  VIII 


who  secured  different  facts  and  attempted  explanations. 

In  a few  animals  the  “germ  plasm”  may  be  morpho- 
logically early  differentiated  and  reasonably  continuous, 
though  governed  by  the-  same  laws  as  other  tissues.  In 
others,  any  part  of  the  general  tissues  may  give  rise  to  a 
complete  organism.  The  behavior  of  some  organisms  is 
intelligent  and  purposeful,  while  that  of  others  is  largely 
mechanical.  Some  structural  responses  of  sessile  organ- 
isms are  advantageous,  some  indifferent  and  some  harm- 
ful. Some  of  the  more  fixed  structures  of  the  highly  indi- 
viduated animals  are  advantageous,  some  indifferent, 
and  some  disadvantageous  (Metcalf,  ’13).  No  other  type 
of  general  statement  appears  to  be  tenable,  yet  each 
extreme  of  each  proposition  has  at  some  time  or  other 
been  the  subject  of  some  all-inclusive  doctrine. 

Such  are  the  limitations  of  an  individual’s  knowledge 
and  the  psychic  limitations  of  our  race  and  generation. 
In  considering  the  psychology  of  religion,  Ames  ( MO, 
p.  394)  points  out  similar  well-recognizable  tendencies  in 
that  field  of  human  activity  and  quotes  Cooley  on  social 
development  as  follows : 

Much  energy  has  been  wasted  or  nearly  wasted,  in  the  exclusive  and 
intolerant  advocacy  of  special  schemes — single  tax,  prohibition,  state 
socialism  and  the  like,  each  of  which  was  imagined  by  its  adherents  to 
be  the  key  of  millennial  conditions.  Every  year  makes  converts  to  the 
truth  that  no  isolated  scheme  can  be  a good  scheme,  and  that  real  prog- 
ress must  be  advanced  all  along  the  line. 

Advance  all  along  the  line  is  what  biological  science 
must  achieve.  This  I believe  means  the  encouraging  of 
all  lines  of  indirect  attack,  whether  they  at  first  throw 
light  on  the  ideal  central  question  of  pure  science  or 
important  practical  problems  or  not.  It  means  the  exer- 
cising of  extreme  caution  in  the  application  of  criteria  of 
values  to  scientific  results.  Such  measures  tend  not  only 
to  stifle  the  best  initiative  in  good  investigators,  but  also 
tend  to  check  the  building  up  of  fruitful  hypotheses. 
The  latter  danger  is  greatest  in  connection  with  the 
mechanistic  criterion  referred  to  above.  As  has  already 
been  stated,  criteria  of  values  can  be  safely  applied  only 


No.  575]  RESPONSES  OF  PLANTS  AND  ANIMALS 


671 


as  broad  general  guides,  and  investigation  should  be 
measured  on  the  basis  of  its  thoroughness,  the  originality 
shown,  etc. 

In  science  special  schemes  of  course  do  not  exist  recog- 
nized as  such,  but  intolerant  application  of  criteria  of 
values  results  in  essentially  the  same  condition.  One 
often  hears  the  statement  made  by  so-called  scientific 
men,  that  this  or  that  line  of  investigation  has  been  pur- 
sued for  several  years,  but  has  failed  to  yield  important 
advances  or  generalizations,  but  they  add,  we  will  be  very 
glad  to  recognize  it  as  soon  as  its  value  is  proven.  This 
seems  to  us*  to  be  a distinctly  unscientific  attitude,  and 
but  a polite  modern  statement  of  a spirit  which  in  former 
generations  often  sent  men  to  the  stake  or  dungeon.  This 
is  true  because  to  these  polite  objectors  its  value  is 
rarely  or  never  proven.  It  is  “schemes”  (preconceived 
theories)  thus  presented  that  have  in  the  recent  past 
stifled  the  study  of  responses  by  discouraging  efforts  in 
that  direction  and  thus  contributed  materially  toward 
making  zoology  the  unorganized  science  which  it  is 
to-day.  We  must  recognize  that  the  various  aspects  of 
zoology  pure  and  applied  have  never  been  well  corre- 
lated, less  so  we  believe  than  in  any  other  branch  of 
natural  science,  clearly  less  than  in  botany.  In  general, 
animal  physiology  has  been  isolated  in  medical  schools 
and  genetics,  faunistics  and  morphology  have  not  been 
properly  influenced  by  it,  while  morphologists  for  many 
years  held  themselves  aloof  from  other  workers. 

In  a discussion  dealing  mainly  with  the  doctrine  of 
natural  selection  in  the  origination  of  adaptations, 
Mathews  (’IS)  has  sounded  the  keynote  of  a growing 
attitude  toward  all  response  questions.  Out  of  the  infi- 
nite different  combinations  which  may  enter  into  the 
proteid  molecule  and  the  varying  rates  at  which  metabolic 
action  may  go  forward,  innumerable  types  of  irritability 
and  correlated  structure  have  been  and  still  are  arising 
under  the  influence  of  environment  external  and  internal. 
Of  these  some  are  incompatible  with  life,  others  indiffer- 


672 


THE  AMERICAN  NATURALIST  [ Vol.  XLYIII 


ent,  and  others  advantageous.  Upon  these  physiological 
characters  natural  selection  has  operated  to  eliminate, 
and  with  time  has  perhaps  rendered  of  less  frequent 
occurrence,  those  characters  that  are  incompatible  with 
their  conditions  of  existence.  External  form,  color  orna- 
mentation, etc.,  while  no  doubt  often  of  importance  them- 
selves are  more  often  the  advantageous  or  indifferent 
correlatives  of  physiological  or  irritability  types  which 
are  compatible  with  their  conditions  of  existence.  The 
study  of  irritability  and  response  may  be  pursued  in 
many  ways — by  experiment,  by  observation  in  nature 
alone  or  combined  with  experiment.  The  mapping  of 
stimulating  conditions  in  nature,  of  the  distribution  of 
types  of  irritability  and  response,  which  is  one  function 
of  field  ecology  and  modern  geography,  can  hardly  fail 
to  contribute  materially  to  the  advance  of  knowledge  in 
many  lines,  including  that  of  the  physico-chemical 
mechanism  of  life.  The  student  of  experimental  ecology 
has  an  infinite  field  of  problems  and  methods  thrown 
open  to  him  by  the  organization  of  such  information 
relative  to  responses.  Still  in  our  attempt  to  make  ad- 
vances along  the  line  of  the  study  of  responses,  we  must 
not  forget  that  it  is  but  one  of  several  lines  of  advance, 
all  of  which  must  sooner  or  later  be  correlated  with  a 
view  to  broader  generalization. 

Hull  Zoological  Laboratory, 

University  of  Chicago, 

April  1,  1914 

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